I put the SR Motorsports hi flow cat without resonator on recently and over time I have become aware of a distinctive exhaust rattle that was not present before. It is more of a high pitched "whiney rattle" if you will as opposed to the rumble described here

https://www.rx8club.com/showthread.p...aust+vibration

but a definite rattle none the less. It was not at all present before the installation of the high flow cat. It basically occurs between 4000 and 5000 RPM only under heavy acceleration or WOT. Not really present before or after that range. In that range the exhaust note change to a rattle note. Did I mention it is very annoying and sounds kinda ricey?

Well of course I have examined the two connections religously. The cat/manifold pipe connection in the front and the rear midpipe/muffler connection and tightened bolts, looked for loose things, rubbing things, heat shield issues, etc., as dicussed here

https://www.rx8club.com/showthread.p...exhaust+rattle

and here

https://www.rx8club.com/showthread.p...exhaust+rattle

The only thing I found was the hanger bar from the rear portion of the midpipe is resting on the flanged frame/transmission support as seen in the first picture. (The second picture actually shows the stock connection in the same area with no rubbing or resting on this support. Note the gap at this connection of the pipes themselves is about the same 1/4 inch gap present with the midpipe setup with the flange/gasket closing the gap.)

Well I put a half inch of rubber from an old tire tube around the hanger bar, secured with wire ties and I even put some dynamat on the flanged frame area so there is no metal making contact but even after doing this I am still getting the rattle. I have checked and rechecked bolts, the heat shields along the entire channel and the heat shield above the muffler, both hot and cold and I cannot find a single area making contact or close to making contact that would seem to be the cause of this rattle. The way it sounds i just don't think it is from the hanger bar and with the rubber and dynamat in between I dont see how it could rattle, and not as loudly and distinctively as it does. It just seems like it has to be coming from somewhere else. This cat/midpipe setup seemed to be just a tad shorter than stock but after installing and tightening there are no gaps are any other apparent abnormalities, it looks pretty much like it did before.

I would like to upgrade the cat back/muffler portion of the exhaust very soon and intend on doing so but it is frustrating that I have not been able to accurately identify or eliminate this rattle, which I would like to do before installing the rest of the exhaust, because if it is somehow still there I will have to start ripping the entire thing off and starting from scratch.

 

I have the same exact rattle that you speak of. My current setup is the Borla exhaust with the SR Motorsports High-Flow cat... It happens even when I let off the throttle and apply the clutch as the rpm's drop.. it happens everywhere now haha.. I have just learned to live with it....

 

Did you do the Borla and the hi flow cat at the same time and is your hanger bar for the cat resting on the flange?

 

I have had my Borla installed for almost 8 months prior to getting the hi flow cat installed. Everything looks fine from below and nobody can find the rattle.. Not sure where it's coming from.

 

So when did the rattle appear after the cat?

 

Had the same problem shortly after installing my Borla exhaust. I took it to a muffler shop and they put it on the lift. The tech banged the exhaust pipes and you could hear the hanger was hitting the frame. He got a blow torch and bent the hanger out of the way alitte. Charged me $10. No more rattles since.

 

Yup.. after I installed the hi flow cat it started.